1. Field of the Invention
This invention relates to new and useful improvements in electrolytic generators and to methods of generating mixtures of oxidizing gases, including oxygen, hydrogen peroxide, ozone, chlorine and chlorine dioxide wherein the generator may be continuously replenished with water and salt during use.
2. Brief Description of the Prior Art
The use of chlorine for disinfecting bodies of water, such as swimming pools, baths, reservoirs, sewage, etc. is well known. In the past, chlorine has usually been supplied by direct application of chlorine gas from tanks containing the gas under pressure. There have also been a number of attempts to provide chlorine gas on a more limited scale by continuous electrolytic generating equipment.
The use of chlorine dioxide in disinfecting bodies of water and in bleaching chemical pulp is well known. Chlorine dioxide is a dangerous and explosive gas and is usually produced as an aqueous solution at the point of usage by chemical decomposition of chlorite salts. The production of chlorine dioxide electrochemically from chlorides is unknown in the literature.
Lindstaedt U.S. Pat. No. 2,887,444 discloses a system in which a body of water, such as, a swimming pool, is provided with a low concentration of dissolved common salt and a stream of water is removed from the main body and electrolyzed to produce chlorine and the chlorine and water stream returned to the main body of water.
Murray U.S. Pat. No. 3,223,242 discloses another type of electrolytic cell for generating chlorine for introduction into a stream of water removed from and introduced back into a swimming pool or other body of water.
Richards U.S. Pat. No. 3,282,823 discloses an electrolytic cell for production of chlorine positioned inline for introducing chlorine into a stream of water removed from and reintroduced into a swimming pool.
Other chlorinating systems using electrolytic cells for production of chlorine for chlorinating bodies of water are shown in Murray U.S. Pat. No. 2,361,663, Oldershaw U.S. Pat. No. 3,351,542, Colvin U.S. Pat. No. 3,378,479, Kirkham U.S. Pat. No. 3,669,857, and Yates U.S. Pat. No. 4,097,356. These electrolytic cells are disclosed in a variety of configurations and most of the cells utilize ion-permeable membranes separating the anode and cathode-containing compartments.
Ion-permeable membrane technology used in electrolytic cells is well developed. Ion-permeable membranes used in electrolytic cells have ranged from asbestos diaphragms to carboxylate resin polymers to perfluorosulfonic acid polymer membranes. The perfluorosulfonic acid membranes were developed by Dupont for use in electrolytic cells. Anion exchange membranes, of polymers having anion functionality, are made by Ionics Inc. of Watertown, Mass.
Dotson U.S. Pat. No. 3,793,163 discloses the use of Dupont perfluorosulfonic acid membranes in electrolytic cells and makes reference to U.S. Pat. Nos. 2,636,851; 3,017,338; 3,560,568; 3,496,077; 2,967,807; 3,282,875 and British Pat. No. 1,184,321 as disclosing such membranes and various uses thereof.
Walmsley U.S. Pat. No. 3,909,378 discloses another type of fluorinated ion exchange polymer used in membranes for electrolytic cells for electrolysis of salt solutions.
Further discussion of membrane technology used in electrolytic cells may be found in Butler U.S. Pat. No. 3,017,338, Danna U.S. Pat. No. 3,775,272, Kircher U.S. Pat. No. 3,960,697, Carlin U.S. Pat. No. 4,010,085 and Westerlund U.S. Pat. No. 4,069,128.
Discussion of perfluorosulfonic acid membranes is also discussed in the technical literature, e.g., Dupont Magazine, May-June 1973, pages 22-25 and a paper entitled "Perfluorinated Ion Exchange Membrane" by Grot, Munn and Walmsley, presented to the 141st National Meeting of the Electro-Chemical Society, Houston, Tex., May 7-11, 1972.
The structure of electrodes used in electrolytic cells is set forth in most of the patents listed above. Additionally, the following U.S. Patents disclose particular configurations of anodes or cathodes used in electrolytic cells.
Giacopelli U.S. Pat. No. 3,375,184 discloses an electrolytic cell with controllable multiple electrodes which are flat plates of wedge-shaped configuration.
Ettel U.S. Pat. No. 3,821,097 discloses the use of flat plates in electroplating cells.
Lohrberg U.S. Pat. No. 3,951,767 discloses the use of flat plate electrolytic anodes having grooves along the bottoms thereof for conducting gas bubbles generated in the electrolytic process.
Andreoli U.S. Pat. No. 565,953 discloses electroplating apparatus having a plurality of metal screens which are not connected in the electric circuit and function to plate out the metal being separated by the electrolysis.
In "The ClO.sub.2 content of chlorine obtained by electrolysis of NaCl", Electrochemical Technology 5, 56-58 (1967) Western and Hoogland report that ClO.sub.2 is not produced in the electrolysis of NaCl in the absence of chlorates.
Sweeney U.S. Pat. No. 4,256,552 discloses an electrolytic generator for production of chlorine, for chlorination of swimming pools, water systems, etc., in which a bipolar electrode is positioned in the anode compartment between the anode and the cation-exchange membrane in the wall separating the compartments.
Sweeney U.S. Pat. No. 4,334,968 discloses improvements on the cell or generator of patent U.S. Pat. No. 4,256,552 and discloses the production of chlorine dioxide in the cell.
Sweeney U.S. Pat. No. 4,248,681 discloses a method of producing chlorine/chlorine dioxide mixtures in the cells of U.S. Pat. Nos. 4,256,552 and 4,334,968 and gives some optimum operating conditions.
Sweeney U.S. Pat. No. 4,308,117 discloses a cell having three compartments, with the anode and cathode in the outer compartments and the bipolar electrode in the central compartment. A cation-exchange membrane is positioned in the wall between the central compartment and the cathode compartment, while an anion-exchange membrane in positioned in the wall between the central compartment and the anode compartment.
Sweeney U.S. Pat. No. 4,324,635 discloses a cell having an anode compartment, a cathode compartment, and a separating wall with a cathode-exchange membrane therein. The cell includes a pump circulating some of the cathode compartment solution to the anode compartment for pH control.
In subsequent studies, it has been found that cells of the type shown in U.S. Pat. Nos. 4,256,552, 4,334,968 and 4,248,681 can be operated with very low salt concentrations and, under such conditions, produce oxidizing gases containing very small amounts of chlorine or chlorine compounds. It has also been found that some means is needed to replenish the water and salt in the cell without having to shut the system down. This invention is directed to the solution of that problem.